The Non‐Ancillary Nature of Trimethylsilylamide Substituents in Boranes and Borinium Cations

The known boranes (R(Me(3)Si)N)(2)BF (R=Me(3)Si 1 , tBu 2, C(6)F(5) 3, o‐tol 4, Mes 5, Dipp 6) and borinium salts (R(Me(3)Si)N)(2)B][B(C(6)F(5))(4)] (R=Me(3)Si 7, tBu 8) are prepared and fully characterized. Compound 7 is shown to react with phosphines to generate [R(3)PSiMe(3)](+) and [R(3)PH](+) (R=Me, tBu). Efforts to generate related borinium cations via fluoride abstraction from (R(Me(3)Si)N)(2)BF (R=C(6)F(5) 3, o‐tol 4, Mes 5) gave complex mixtures suggesting multiple reaction pathways. However for R=Dipp 6, the species [(μ‐F)(SiMe(2)N(Dipp))(2)BMe][B(C(6)F(5))(4)] was isolated as the major product, indicating methyl abstraction from silicon and F/Me exchange on boron. These observations together with state‐of‐the‐art DFT mechanistic studies reveal that the trimethylsilyl‐substituents do not behave as ancillary subsitutents but rather act as sources of proton, SiMe(3) and methyl groups.